/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.io;

import java.io.IOException;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.DataInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ByteArrayInputStream;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.InflaterInputStream;

/**
 * A base-class for Writables which store themselves compressed and lazily
 * inflate on field access. This is useful for large objects whose fields are
 * not be altered during a map or reduce operation: leaving the field data
 * compressed makes copying the instance from one file to another much faster.
 */
public abstract class CompressedWritable implements Writable {
	// if non-null, the compressed field data of this instance.
	private byte[] compressed;

	public CompressedWritable() {
	}

	public final void readFields(DataInput in) throws IOException {
		compressed = new byte[in.readInt()];
		in.readFully(compressed, 0, compressed.length);
	}

	/**
	 * Must be called by all methods which access fields to ensure that the data
	 * has been uncompressed.
	 */
	protected void ensureInflated() {
		if (compressed != null) {
			try {
				ByteArrayInputStream deflated = new ByteArrayInputStream(
						compressed);
				DataInput inflater = new DataInputStream(
						new InflaterInputStream(deflated));
				readFieldsCompressed(inflater);
				compressed = null;
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
	}

	/** Subclasses implement this instead of {@link #readFields(DataInput)}. */
	protected abstract void readFieldsCompressed(DataInput in)
			throws IOException;

	public final void write(DataOutput out) throws IOException {
		if (compressed == null) {
			ByteArrayOutputStream deflated = new ByteArrayOutputStream();
			Deflater deflater = new Deflater(Deflater.BEST_SPEED);
			DataOutputStream dout = new DataOutputStream(
					new DeflaterOutputStream(deflated, deflater));
			writeCompressed(dout);
			dout.close();
			deflater.end();
			compressed = deflated.toByteArray();
		}
		out.writeInt(compressed.length);
		out.write(compressed);
	}

	/** Subclasses implement this instead of {@link #write(DataOutput)}. */
	protected abstract void writeCompressed(DataOutput out) throws IOException;

}
